Propylene dimerization process

ABSTRACT

A process for the dimerisation and codimerisation of olefines, consists in maintaining the olefine or olefines in an inert solvent in contact with a catalyst system comprising a complex formed by a halide of a transition metal of Group VIII, complexed with 1 to 6 molecules, per atom of transition metal, of an organic sulphoxide or disulphoxide, the complex being accompanied by an organoaluminium compound. The process can be carried into effect in accordance with two variants: EITHER THE CATALYST IS PREPARED IN SITU, WHICH REQUIRES AN Al/transition metal atomic ratio which is between 3 and 9 to 1, or the catalyst is prepared ex situ (continuous process), which requires an Al/transition metal ratio greater than 9 to 1.

United States Patent [191 Desgrandchamps et al.

[ 51 Jan. 30, 1973 PROPYLENE DIMERIZATION PROCESS Inventors: GuyDesgrandchamps, Luxembourg;

Henri Hemmer, Billere; Michel Haurie, Pau, all of France Societe Anonymedite: Societe Nationale des Petroles DAquitaine, Courbeuoie, FranceFiled: Jan. 13, 1970 Appl. No: 2,653

Assignee:

Foreign Application Priority Data Jan. I6, 1969 France ..6900607 U.S.CI. ..260/683.l5 D, 252/43] R Int. Cl ..C07c 3/10 Field of Search..260/683.I5 D

References Cited UNITED STATES PATENTS 4/1968 Wilke ..260/683.l5 X

3,558,736 I/I97l Berge m et al. ..260/683.I5

Primary ExaminerPaul M. Coughlan, .Ir.

Al!orneyM ilton 1. Wayne 57 ABSTRACT The process can be carried intoeffect in accordance with two variants: EITHER THE CATALYST IS PREPAREDIN SITU, WHICH REQUIRES AN Al/transition metal atomic ratio which isbetween 3 and 9 to I, or the catalyst is prepared ex situ (continuousprocess), which requires an Al/transition metal ratio greater than 9 to1.

12 Claims, No Drawings PROPYLENE DIMERIZATION PROCESS The inventionincludes novel catalysts as defined above for the dimerisation andcodimerisation of olefines.

This invention relates to the dimerisation and codimerisation ofolefines.

It is one object of the invention to provide an improved process for thedimerisation or codimerisation, in liquid phase, of olefines,particularly lower olefines, that is olefines having two, three or fourcarbon atoms.

Another object is to provide such a process for the dimerisation ofpropylene, with the object of obtaining a product which is rich inmethyl pentenes.

A still further object of the invention to provide novel catalysts whichare suitable for use in the dimerisation or codimerisation of olefines.

The dimerisation of lower alpha-olefines represents an importantindustrial problem, to which considerable research has been applied inrecent years. Its principle object is the production of C and Colefines, the subsequent pyrolysis of which yields dienes which are ingreat demand for the manufacture of elastomers; this is particularly thecase with isoprene and butadiene, which are obtained from methylpentenes and butenes. A basic problem in this technique has been to findsuitable catalysts, especially ones which will enable the loweralpha-olefines to be dimerised in solution with a good selectivity asregards the desired dimers, including particularly the dimerisation ofethylene into butenes and that of propylene into hexenes.

Despite the number and the variety of the compounds which have so farbeen tried or used the problem still calls for improvements, becauseeach of the types of catalysts tried had certain defects, as well asadvantages.

The present invention provides a number of useful improvements. Theseinclude particularly the provision and use of catalysts which are easyto prepare and the optimum degree of activity of which is found at thetemperatures which can be most easily regulated, that is to say at, ornot far from, C. It is known that, because of the latent heat of fusionof ice, it is at 0 C., or close to this temperature, that it is easiestto keep constant the temperature of the medium in an exothermicreaction. It is also in this region near 0 C. that the catalysts of thepresent invention have been found to have good selectivities for thedimers, relatively to the higher oligomers, as compared with those ofthe prior art. These selectivities can exceed 95 percent, this beingobtained for a practically quantitative conversion.

Because of the temperature at which the operation takes place, thedimers contain a high proportion of 2- methyl-pent-Z-ene, which isparticularly required for the preparation of isoprene. The amount can bemore than 70 percent in the dimer which is obtained.

The productivity can exceed 200 kg/g of nickel per hour for operationscarried out continuously, when nickel is the transition metal of thecatalyst used.

The new catalyst according to the invention is characterized in that itcomprises a complex formed by a halide of a transition metal of GroupVIII of the Periodic Table, complexed with from I to 6 molecules, peratom of transition metal, of an organic sulphoxide or disulphoxide, thiscomplex being accompanied by an organoaluminum compound, preferably analkyl aluminum halide.

The sulphoxide complex of the transition metal in the catalyst of theinvention can be represented by formulas of the type MX p(R,(SO),,R orl\vfX p(R,SOR SOR in which M is a transition metal of Group VIII, thepreferred metals being iron, cobalt, nickel and copper, and particularlynickel, while X is a halogen, particularly chlorine, bromine or iodine,and p is from 1 to 6. The number of sulphoxide molecules which can becomplexed to MX depends on the conditions under which the complex isprepared. Thus n may be 1 or 2 and R R and R can be alkyl, cycloalkyl oraryl groups and they may be the same or different.

Sulphoxides which are particularly suitable for the preparation of thecatalysts of the present invention include dicyclohexyl sulphoxide,diphenyl sulphoxide, dimethyl-1,2-dhioethane oxide CH3-S'-(CH2)2--SCH3(l ll but other sulphoxides may also be used.

According to one preferred feature of the invention, the speed ofactivation of the catalysts and, as a result, the speed of reaction canbe improved, without the selectivity being lowered, by adding a smallquantity of water to the catalyst system. This quantity should, for bestresults, be between the very strict limits of O to 2 moles of H 0 permole of nickel complex, because beyond these limits, the water has aharmful effect, causing a fall in the selectivity rate.

Sulphoxide complexes based on transition metals, particularly nickel,can be easily prepared by the methods described in the followingexamples.

It is interesting to find that the very good results which are obtainedusing the process of this invention, as regards the degree ofconversion, the dimer selectivity relatively to the oligomers formed andthe reaction time, only occur when the catalyst contains a transitionmetal halide complexed with an organic sulphoxide as defined above. Ifthe inclusion of this complex in the reaction medium is replaced by thesole addition of the transition metal halide and an organoaluminumcompound, the reaction is much slower than with the complex.

For example, if the transition metal halide is nickel chloride, 24minutes are needed, in the presence of 6 molecules of water, to obtain aconversion of percent. The proportion of higher oligomers relatively tothe dimers is large.

If the addition of the complex of the present invention into thereaction medium is replaced by the simultaneous addition of nickelchloride and diphenyl sulphoxide, there is obtained an improvement inthe dimer selectivity, but the reaction time has always been found to befrom 30 to 40 minutes, that is to say more than l0 or 20 times slowerthan with a catalyst according to the invention.

On the other hand, to use a catalyst formed by the simultaneous additionof nickel chloride and sulphoxide (without the addition of water), itwould be necessary to allow from to 200 minutes to obtain a conversionrate of only 50 percent.

The organic aluminum compounds which are suitable for carrying theinvention into effect, concurrently with the nickel complexes asindicated above, can in general be similar to those which havepreviously been used by themselves. They include particularly compoundsof the general formulas R AlX, RAlX and R Al X? The radical R isgenerally an alkyl; alkyls such as ethyl, propyl, isopropyl, butyl orisobutyl are particularly suitable. The halogen X is generally chlorineand/or bromine.

Although the proportion of the organoaluminum compounds can varyrelatively to that of the nickel complex within limits which are between3 and 100 to 1, it is preferable for the Al/transition metal atomicratio in the catalyst systems to be between 6 and 12 and better stillbetween 7 and 9 to 1, when the catalyst is prepared in situ, that is tosay, when the sulphoxide complex of the transition metal, the solvent,the organic aluminum compound and the olefine are introducedsimultaneously into the autoclave. On the other hand, it is preferablefor this ratio to be higher than 9 to 1 and for it preferably to bebetween l5 and 50 and, even better, between 20 and 30 to 1 when thecatalyst is prepared ex situ, that is to say, before it is brought intocontact with the olefine which is to be dimerized. It is within theselimits that the best selectivity is obtained.

For a catalyst prepared in situ, the quantity of catalyst can be suchthat the weight of the transition metal of the complex being employedrepresents 0.05g to 5g, in the case of nickel, per kg of olefinessubjected to the dimerization. Excellent results are obtained withnickel contents from 0.1g to lg of nickel per kg of olefine. In the caseof a catalyst prepared ex situ, this nickel content is preferably form0.005g to lg; excellent results are obtained with contents from 0.00lgto 0.5g.

The dimerization according to the process of the invention can becarried out at temperatures of from 50 to +80 C., but the most practicalresults are obtained between 5 and +1 C. Very good results, withconversions are practically 100 percent, are obtained at 0 C. Since itis this temperature which, for the reason referred to above, is theeasiest to keep constant, it represents the temperature which is by farthe preferred temperature for carrying out the present invention.

The solvents suitable for the dimerization which has been described arethe liquids which are neutral with respect to the catalysts and includeparticularly the'optionally halogenated saturated hydrocarbons, thearomatic or halogenated aromatic hydrocarbons; aliphatic or aromatic orcyclic ethers which are not reactive as regards the catalysts can alsobe used.

The usual solvents known in the art are generally suitable. It is thuspossible, for example, to use toluene, xylene, chlorobenzenes,chloronaphthalenes. Halogenated aromatic solvents are preferred becausethey lead to high reaction speeds and because of the better solubilityin them of the catalyst system. Liquid propylene can also serve as asolvent as well as forming the dimers produced in the reaction.

It is advisable to select a solvent which has a fairly high boilingpoint and a sufficiently low solidification point so that the dimersformed can easily be separated after the reaction without there beingany fear of solidification at the low temperatures at which thedimerization takes place. Consequently, according to one 'of thefeatures of the invention, the solvent being used is preferably amonohalonaphthalene or dihalonaphthalene, and more particularlyalphachloronaphthalene, the boiling point of which is 259 C. with asolidification point of 20 C.

The process of the invention can be carried into effect in accordancewith either of two variants. It is possible to use either a process insitu, that is to say, to introduce the catalyst, solvent, organicaluminum compound and olefine simultaneously into the reactor, or an exsitu process, which permits of continuous operation.

The operating procedure according to the first variant of the inventioninvolves effecting the dimerization or codimerization of the olefines inan in situ process.

In the following Examples 4 to 13, there will be described test carriedout in a stainless steel autoclave with a capacity of 125 ml, equippedwith a double jacket for cooling purposes. A specified quantity of thenickel sulphoxide complex was introduced into the autoclave in anatmosphere of nitrogen. A certain volume of alpha-cloronaphthalene and aspecified quantity of ethyl aluminum sesquichloride Al Et Cl were theninjected. A given weight of liquid propylene was condensed in theautoclave, which was cooled to 0 C.

The drop in the pressure of the propylene in the autoclave, due to thedimerization continued until from 90 to 100 percent of the propylene haddisappeared. At the end of the reaction, the catalyst was deactivated byadding 10 ml of water. The organic phase was extracted and subjected todistillation. The conversion of the initial propylene and thecomposition of the formed products were established, this enabling theselectivity of dimers relatively to the upper oligomers to be expressed.

The operating procedure in accordance with the second variant of theinvention enables conversion rates and selectivities to be obtainedwhich are as good as in the in situ process. It involves preparing theactivated catalyst before it is brought into contact with the olefine.This process, which permits of continuous operation, has a certainnumber of other advantages; it is based on a number of observations madeby the inventors. The authors of the present invention have in factobserved that when the catalyst is preparedex situ, that is to say,before it is brought into contact with the olefme which is to bedimerized the Al/transition' metal atomic ratios which are necessary forobtaining the best results are different from those which are necessaryfor obtaining the same results when the catalyst is prepared in situ.The value of this ratio has to be appreciably increased; the quantity ofnickel necessary for the dimerization of olefines is much less than thatused in the process carried out in situ. From an economic point of view,this constitutes a great advantage, when the high cost of the nickel istaken into account.

The process in accordance with this second variant involves preparing acatalyst of the formula MX pR,(S 0),,R or MX p(R SOR SOR activating thiswith an organoaluminum compound, so that the transition metal andaluminum elements are in an atomic ratio equal to or greater than 9 to land in using this catalyst under conditions in which it has beenprepared before being used with the olefine or olefines to be dimerized.

The nickel complexes as described above are not directly active in thisform. For making these complexes active, the transition metal(preferably nickel) has to be reduced to a lower valency state by meansof the organoaluminum compound. The inventors of the present inventionhave found that the activation of the sulphoxide complex by theorganoaluminum compounds is not instantaneous, but that it can last fromto 30 minutes.

Thus, when operating by bringing the nickel complex, organoaluminumcompound, solvent and propylene simultaneously into the reactor, theactive form of the catalyst is only gradually liberated. The quantity ofnickel which has actually participated in the catalysis is much smallerthan the quantity engaged in the complex.

In the presence of the active complex, the reaction can be extremelyrapid and even violent; it can be of the order of 2 to 3 minutes. Whenusing the in situ process, the quantity of transition metal introducedinto the catalyst is chosen so that the organoaluminum compoundliberates, in 2 or 3 minutes, the quantity of active complex necessaryfor the reaction. Since the activating reaction lasts from l0 to 30minutes, it can be seen that the quantity of transition metal in thecatalyst is about 5 to times larger than that which has actually servedfor the reaction.

The reaction time is, in part, a function of the quantity of nickelwhich is present. However, there is no advantage in this nickel contentbeing too large, because a very rapid reaction is also very violent andthere is a danger of a certain quantity of the nickel not being used. Itis preferable to select quantities of nickel for which the productivityis best. The quantity of catalyst can be such that the weight oftransition metal of the complex employed represents 0.005g to lg, in thecase of nickel, per kg of olefine being subjected to the dimerization orcodimerization excellent results are obtained with nickel contents offrom 0.0lg to 0.5g.

For preparing such a catalyst, the inactive complex and theorganoaluminum halide are brought together in suspension in a solvent.

The sulphoxide complex is insoluble in the solvents which areparticularly suitable for the dimerization A homogeneous solution isonly obtained after these complexes have been activated with theorganoaluminum halide. For obtaining an efficient catalyst, it isnecessary for this activation to be effected in the presence of aprotecting olefine. It is thought that this olefine, by beingcoordinated with the nickel atom of the active complex, stabilizes thelatter and prevents its decomposition into metallic nickel.

A number of olefines can be used with advantage to this end, but aparticular preference, as regards the preparation of the catalyst, isgiven to the use of propylene dimers. This use avoids the introductionof a supplementary compound which is foreign to the reaction and whichit would subsequently be necessary to separate out. However, as theactive complex is only sparingly soluble in these solvents, it isnecessary to work in the presence of a more or less large quantity ofthis solvent, which will permit the obtaining of catalyst solutionswhich are not too dilute.

One preferred solvent is formed, for example, of onethird of propylenedimers and two-thirds of chlorobenzene. The quantity of complex whichcan be dissolved in this solvent corresponds to approximately 1 to 3milliatoms of nickel per liter.

It is important that the activating reaction and also the preservationof the activated catalyst should occur in an inert atmosphere, forexample argon, because the catalyst solutions are extremely sensitive tothe oxygen of the air (which causes the precipitation of the metallicnickel) and to humidity (which hydrolyzes the ac tive complex). Theactivation of the sulphoxide complex can be followed qualitatively bythe change in color, the inactive form being blue and the homogeneousactive solution being yellow.

The activation of the catalyst complex can be effected at differenttemperatures which may extend from to +20 C. The activation speedincreases with the temperature. However, for the sake of goodpreservation of the catalyst, it is preferable to work at a lowtemperature. By way of example for a temperature of 20 C., the timerequired for activation can reach a few hours. The time is only a fewtens of minutes when the activation is effected at -l0 C. and it is onlya few minutes for a temperature of 0 C.

When the active catalyst solution has been prepared, it is preserved ata low temperature in an argon atmosphere. The stability of this solutionenables it to be kept for several days. Nevertheless, it is preferred touse it in the few hours which follow its preparation and, better still,during the first hour. During the operation of dimerizing orcodimerization the olefines, the withdrawal of this solution and itsintroduction into the reactor have to be carried out protected from air.The olefine to be dimerized or codimerized is then injected, at aconstant pressure, into the cooled reactor.

The examples which follow illustrate certain forms of the invention,without however limiting it.

EXAM PLE 1 Preparation of the NiCl p(C H,,) SO complex.

lg of NiCl '6H O is suspended in 80 ml of 2,2- methoxypropane; heatingtakes place in a nitrogen atmosphere at C. for 2 hours. A yellowishprecipitate is obtained, corresponding to 0.04 mole of anhydrous NiClThe supernatant liquid is distilled and the anhydrous NiCl placed insuspension in 2,2-dimethoxypropane, is treated with a very large excessof dicyclohexyl sulphoxide in solution in benzene. The precipitate whichis formed is heated under reflux in the suspension for 12 hours. Thecomplex is filtered, washed 3 times with anhydrous ether and dried undervacuum.

This complex has an infra-red spectrum which is characterized by theline at 980", which corresponds to that of the SO group coordinated withoxygen to the transition metal. One of the infra-red lines of (C H S0 isl,030l,020""", corresponding to the free SO group.

EXAMPLE 2 Preparation of the NiCl p(C H SO complex.

1.5 g (0.01 mole) of anhydrous NiCl and 7.5 g (0.03 mole) of (C H SO areintroduced into a spherical flask. This is heated for 2 hours at C.,this being a temperature slightly higher than the melting point of (C HQSO; a green solution is obtained, which is filtered hot in order toeliminate any NiCl which has not reacted; 25 ml of benzene are added; aprecipitate is formed, which is filtered, washed with benzene and withanhydrous ether, and dried under vacuum. As in the preceding example,this complex has an infra-red spectrum characterized by the line at 980EXAMPLE6 In an operation similar to that of Examples 4 and 5,

EXAMPLE 3 0.7 X 10' moles of 5 Preparation of the I 5 2 1 Niel, out-scums cm) II II 0 complex.

5.l0"moles of (Al Et Cl (the Al/Ni ratio of which is 7 This preparationis described in the Journal of the 9 and 10 ml of chlombenzene are used;8 of South African Chemical Institute, volume XXl-8-l hqu'd Propyleneare added After '3 mmutes the 968 conversion of the propylene intoliquid oligomers is Anhydrous Nick Suspended in a nitromethane' istotal. The quantity of dimers recovered is then 25.4g added to a hotsolution of nitromethane containing an a selecuv'ty of 83 percent Thesedlmers are comexcess of posed of72.5 percent of methyl pentenes, 23.8percent of hexenes and 3.7 percent of dimethyl butenes.

C 3|s'( 7)7fiCHu EXAMPLE 7 Operations identical with those of Example 5,are This mixture is allowed to react between 95 and 100C carried out atdifferent temperatures. Their results for 1 hour. Green crystals ofgiven together, are as follows:

Conver- Se1ecsion, tivity, Methyl Dimethyl Temp., C Time percent percentHexenes pentenes butenes 20 60hrs 7s 90 14.3 85.7

hrs. s7 92 14.4 85.6 0 3hrs 98 85 24.1 72.6 3.3 2.30 min... 96. 5 9o 22.4 75. 2 2. 4 +10 1.20 min.-- 93 81.5 28.5 66.7 4.8

NiClz C az)2SCII;i These examples show that an increase in temperal Hture favors the conversion of the propylene, but to the detriment of theselectivity. precipitate by cooling.

Like the foregoing, these crystals have an infra-red EXAMPLE 8 Spectrum,characterized y the line at In operations similar to those of Example 5,the

EXAMPLE 4 Nl(.'lg(Cllzi (Giff); mi.)

. 1 Process in which the catalyst is prepared in situ (Vari- 0 ant l Thecatalyst comprises 810 mg of the NiCl p(C H,, q p replaced elther y theaddltlotlpf y a )ZSO comp]ex and 5 X -3 moles f ethyl aluminum NiCl byitself or by the simultaneous addition of NlC'l sesquichloride Thequantity of a|pha and disulphoxide or by the simultaneous addition ofchloronaphthalene is 15 ml and that of the added liquid N1Cl2H2O fsulphoxlde' propylene is 30.6g. After one minute, 94 percent of the Thefollowmg results are obtamed' propylene is transformed into 28.7g Ofliquid oligomers, from which 20.6g of C dimers are isolated, with aselectivity of 72 percent. The dimers WhlCh are obtained are composed of74.2 percent of methyl pen- Niclfiudisulphoxidc) 02 hrs 50 82 tenes,20.2 percent of hexenes and 5.6 percent of Nicl -l-(disulphoxide) 130hrs 50 39 dimethyl butenes. NiClr6H0 24 hrs 90 76NiCl,6H,O+3(disulphoxidc) 30 hrs 92 92 EXAMPLE 5 Using the NiCl p(C H SOcomplex, 5.15 mg of it are employed, together with 5 X 10' moles of AlEt Cl The solvent is constituted by 10 ml of alphachloronaphthalene.30.6g Of liquid propylene are added. After 2.30 minutes at 0C thequantity of liquid oligomers obtained is 29.5g, which corresponds to aconversion of 96.5. The quantity of dimers recovered is 26.5g, with aselectivity of 90%. These dimers are composed of 75.2 percent of methylpentenes, 22.4 percent of hexenes and 2.4 percent of dimethyl butenes.

EXAMPLES 9 T013 The following Examples are intended to illustrate theinfluence of the presence of small quantities of water in the catalyst.The operations are carried out under the same conditions as those ofExample 5; the number of molecules of water per molecule of complex isindicated in the Table. In order to be able to appreciate better theinfluence of the presence of water on the reaction time, g of propylenewere used, instead of 30g.

Example Mol of H per Time Conver- Selec- No mole of complex sion tivity9 0 32 hrs 98 90 10 l 25 hrs 95 89.5 11 2 hrs 94 88.5 12 3 9 hrs 92 8513 4 5 hrs 91 84 The above shows that the addition of water reduces thetime of reaction, without it reducing the selectivity, provided that notmore than 2 moles of H 0 per mole of complex nickel are added.

EXAMPLE 14 Process in which the catalyst is prepared ex situ (variant 2)Preparation of an active catalyst solution 0.5l5g of the NiCl p(C H SOcomplex are introduced under a purified argon atmosphere into athree-necked spherical flask. The complex is suspended while stirring in800 ml of a solvent, which is formed of one-third of propylene dimersand two-thirds of chlorobenzene, and is carefully dried and distilledunder argon. The reactor is kept at a temperature of 0 C. and X 10'moles of Al Et Cl are added dropwise.

The activation is followed quantitatively by the change in color of thesolution, which changes from blue to yellow. This catalyst solution iskept under argon at 0 C. until the moment when it is used.

EXAMPLE 15 Dimerisation Into a 250 ml stainless steel autoclave, kept at0 C. by circulation of a thermostatically controlled liquid through adouble jacket, there are introduced under an argon atmosphere 40 ml ofthe previously prepared active catalyst solution. 30.6 g of propyleneare added; the temperature is kept at 0 C. The initial pressure is 5bars. The decrease in pressure permits the advance of the reaction to befollowed. When the pressure falls to O, the reaction is terminated. Then10 ml of water are added to deactivate the catalyst. The organic phaseis separated and distilled. The conversion of the propylene is thencomplete. The selectivity is calculated according to the dimerscollected. The quantity of collected dimers is 25.9g, which gives aselectivity of 88 percent. These dimers are composed of 75 percent ofmethyl pentenes, 23 percent of hexenes and 2 percent of dimethylbutenes.

We claim:

1. A process for the dimerization of propylene which comprisesmaintaining said propylene in an inert solvent in contact with acatalyst system at a temperature of from 50 to C. to effect dimerizationwherein said catalyst system includes from 0 to 2 moles of water permole of a complex metal selected from the group consisting of MXp(R(SO),,R) and in which M is a metal selected from the group consistingof iron, cobalt, nickel, and copper; X is halogen;p is an integer from 1to 6; n is l or 2; and R is a member selected from the group consistingof alkyl, cycloalkyl and aryl, and an organoaluminum compound.

2. A process according to claim 1, wherein the catalyst is prepared byintroducing simultaneously the sulphoxide complex of said metal, saidsolvent and an organoaluminum compound and said propylene into areaction vessel where said dimerization is being effected and the atomicratio between the aluminum and said metal present in the catalyst isfrom 6 to 12.

3. A process according to claim 1, wherein said metal is nickel and thequantity of catalyst used corresponds to 0.05g to 5g of nickel per kg ofpropylene being dimerized.

4. A process according to claim 1, wherein the catalyst is prepared bytreating a sulphoxide complex of said metal and an organoaluminumcompound and the atomic ratio between the aluminum and said metalpresent in the catalyst is in excess of 9 up to 50.

5. A process according to claim 4, wherein the catalyst system containsfrom 1 to 3 milliatoms of said metal per liter.

6. A process according to claim 4, wherein the catalyst system containsfrom 1 to 3 milliatoms of said metal per liter, wherein the said metalis nickel and wherein the quantity of catalyst used corresponds to0.005g to 1g of nickel per kg of olefine being dimerized or codimerized.

7. A process according to claim 1, wherein the said metal is nickel.

8. A process according to claim 1 wherein the dimerization reaction iseffected in a halogenated aromatic hydrocarbon solvent.

9. A process according to claim 2, wherein the atomic ratio between thealuminum and said metal present in the catalyst is from 7 to 9.

10. A process according to claim 3, wherein the quantity of catalystused corresponds to 0.1g to lg of nickel per kg of propylene.

11. A process according to claim 4, wherein the atomic ratio between thealuminum and said metal present in the catalyst is between 15 and 50.

12. A process according to claim 1 wherein the catalyst system isprepared in a halogenated aromatic hydrocarbon solvent.

1. A process for the dimerization of propylene which comprises maintaining said propylene in an inert solvent in contact with a catalyst system at a temperature of from -50* to +80* C. to effect dimerization wherein said catalyst system includes from 0 to 2 moles of water per mole of a complex metal selected from the group consisting of MX2p(R(SO)nR) and in which M is a metal selected from the group consisting of iron, cobalt, nickel, and copper; X is halogen; p is an integer from 1 to 6; n is 1 or 2; and R is a member selected from the group consisting of alkyl, cycloalkyl and aryl, and an organoaluminum compound.
 2. A process according to claim 1, wherein the catalyst is prepared by introducing simultaneously the sulphoxide complex of said metal, said solvent and an organoaluminum compound and said propylene into a reaction vessel where said dimerization is being effected and the atomic ratio between the aluminum and said metal present in the catalyst is from 6 to
 12. 3. A process according to claim 1, wherein said metal is nickel and the quantity of catalyst used corresponds to 0.05g to 5g of nickel per kg of propylene being dimerized.
 4. A process according to claim 1, wherein the catalyst is prepared by treating a sulphoxide complex of said metal and an organoaluminum compound and the atomic ratio between the aluminum and said metal present in the catalyst is in excess of 9 up to
 50. 5. A process according to claim 4, wherein the catalyst system contains from 1 to 3 milliatoms of said metal per liter.
 6. A process according to claim 4, wherein the catalyst system contains from 1 to 3 milliatoms of said metal per liter, wherein the said metal is nickel and wherein the quantity of catalyst used corresponds to 0.005g to 1g of nickel per kg of olefine being dimerized or codimerized.
 7. A process according to claim 1, wherein the said metal is nickel.
 8. A process according to claim 1 wherein the dimerization reaction is effected in a halogenated aromatic hydrocarbon solvent.
 9. A process according to claim 2, wherein the atomic ratio between the aluminum and said metal present in the catalyst is from 7 to
 9. 10. A process according to claim 3, wherein the quantity of catalyst used corresponds to 0.1g to 1g of nickel per kg of Propylene.
 11. A process according to claim 4, wherein the atomic ratio between the aluminum and said metal present in the catalyst is between 15 and
 50. 